5.4 Namf_MT Service

29.5183GPP5G SystemAccess and Mobility Management ServicesRelease 16Stage 3TS

5.4.1 Service Description

Namf_MT service allows a NF to request information related to capabilities to send MT signalling or data to a target UE. The following are the key functionalities of this NF service

– paging UE if UE is in IDLE state and respond other NF after the UE enters CM-CONNECTED state.

– response to the requester NF if UE is in CONNECTED state.

– providing the terminating domain selection information for IMS voice to the consumer NF.

5.4.2 Service Operations

5.4.2.1 Introduction

For the Namf_MT Service the following service operations are defined:

– EnableUEReachability

– ProvideDomainSelectionInfo

5.4.2.2 EnableUEReachability

5.4.2.2.1 General

The EnableUEReachability service operation is used in the following procedure:

– MT SMS over NAS in CM-IDLE state (see 3GPP TS 23.502 [3], clause 4.13.3.6), or in CM-CONNECTED state (see 3GPP TS 23.502 [3], clause 4.13.3.7).

– UPF anchored Mobile Terminated Data Transport in Control Plane CIoT 5GS Optimisation (see clause 4.24.2 of 3GPP TS 23.502 [3]).

The EnableUEReachability service operation shall be invoked by the NF Service Consumer (e.g. SMSF, SMF) to enable the reachability of the UE.

The NF Service Consumer shall invoke the service by using the HTTP method PUT, towards the URI of a "ueReachInd" resource as specified in clause 6.3.3.2. See also figure 5.4.2.2.1-1.

Figure 5.4.2.2.2-1: NF Service Consumer enables the reachability of the UE

1. The NF Service Consumer sends a PUT request to the resource representing the ueReachInd resource of the AMF. The payload body of the PUT request shall contain an "EnableUeReachabilityReqData" object.

2a. On success:

– if the UE is in CM-CONNECTED state, the AMF shall immediately respond using "200 OK" status code, with payload containing an "EnableUeReachabilityRspData" object.

– if the UE is in CM-IDLE state and the NAS message is to be sent over via 3GPP access, the AMF shall page the UE. When UE becomes CM-CONNECTED, "200 OK" shall be returned with payload containing an "EnableUeReachabilityRspData" object.

2b. On failure or redirection, one of the HTTP status code listed in Table 6.3.3.2.3.1-3 shall be returned. For a 4xx/5xx response, the message body shall contain a ProblemDetails or ProblemDetailsEnableUeReachability structure with the "cause" attribute set to one of the application error listed in Table 6.3.3.2.3.1-3.

The AMF shall respond with the status code "403 Forbidden", if the UE is in a Non-Allowed Area and the service request is not for regulatory prioritized service. The AMF shall set the application error as "UE_IN_NON_ALLOWED_AREA" in POST response body.

5.4.2.3 ProvideDomainSelectionInfo

5.4.2.3.1 General

The ProvideDomainSelectionInfo service operation shall be invoked by the NF Service Consumer (e.g. UDM) to get the UE information for terminating domain selection of IMS voice, including following information:

– Indication of supporting IMS voice over PS Session;

– Time stamp of the last radio contact with the UE;

– Current Access type and RAT type

The NF Service Consumer shall invoke the service by using the HTTP GET towards the URI of the "UeContext" resource (See clause 6.3.3.3.3.1). See also figure 5.4.2.3.1-1.

Figure 5.4.2.3.1-1: Provide UE Information for Terminating Domain Selection

1. The NF Service Consumer shall send a GET request to the URI of the "UeContext" resource on the AMF, with query parameter "info-class" set to value "TADS".

2a. On success, the AMF shall return "200 OK" status code with payload containing an "UeContextInfo" data structure including UE information for terminating domain selection for IMS voice.

2b. On failure or redirection, one of the HTTP status code listed in Table 6.3.3.3.3.1-3 shall be returned. The message body shall contain a ProblemDetails object with "detail" set to one of the corresponding application errors listed in Table 6.3.3.3.3.1-3.